How to define a colorband in Blender 2.74 using python script
Cycles and Blender Internal render engines have a different Materials ecosystem. They're similar in many ways, but different on important details.

Blender Internal

import bpy

mat = bpy.data.materials.new('experiment')
mat.use_diffuse_ramp = True
elem = mat.diffuse_ramp.elements.new(0.25)
elem.color = (1,0.2,0.3,0.3)


Cycles

Involves adding nodes, or appending a premade material from a different .blend (also easy but a different topic)

import bpy

mat = bpy.data.materials.new('experiment4')
mat.use_nodes = True

ramp_node = mat.node_tree.nodes.new('ShaderNodeValToRGB')
elements = ramp_node.color_ramp.elements

elem = elements.new(0.25)
elem.color = (1,0.2,0.3,0.3)

# the default 'new material' always has a 'Diffuse BSDF' node, 
# here we obtain a reference to it
diffuse_node = mat.node_tree.nodes['Diffuse BSDF']

# nodes need to be hooked up!
mat.node_tree.links.new(ramp_node.outputs[0], diffuse_node.inputs[0])


The reason I mention appending an existing material is because it can be a lot more convenient to tailor a complex material once and use many variations of it in subsequent blends by appending the material and adjusting known values. Scripting Cycles materials can be a little verbose :)

If you still have questions then hopefully you'll have some idea what to ask about.